This invention related to a dock leveler mechanism including an upwardly biased ramp that is pivotably interconnected with a base for movement between raised and lowered positions, and more particularly to an automatic release feature for a holddown mechanism that selectively maintains the ramp in a lowered position and enables upward movement of the ramp in response to application of an upward force on the ramp when the ramp is in a lowered position.
A dock leveler assembly typically includes a base mounted to a loading dock or the like, and a ramp pivotably mounted to the base for movement between raised and lowered positions. A biasing arrangement, such as a spring arrangement, is interposed between the ramp and the base for biasing the ramp upwardly toward a raised position. A holddown mechanism is interposed between the base and the ramp, for selectively maintaining the ramp in a lowered position, such as when the outer end of the ramp is engaged with the bed of a truck to enable unloading of the truck. When the dock leveler is not in use, the holddown mechanism maintains the ramp in a position level with the dock against the force of the biasing arrangement. The holddown mechanism typically includes a first member that is pivotably interconnected with the base and a second member that is extendible and retractable relative to the first member and that is pivotably interconnected with the ramp. A releasable engagement arrangement is interposed between the first and second members, for selectively fixing the position of the second member relative to the first member and thereby maintaining the position of the ramp relative to the base, for maintaining the ramp in a lowered position against the force of the biasing arrangement.
The holddown mechanism includes a release member that interacts with the releasable engagement arrangement, for selectively disengaging the releasable engagement arrangement to enable the second member to be extended relative to the first member, and to thereby allow the ramp to be moved to a raised position. The release member is movable from an inoperative position, in which the releasable engagement arrangement is engaged, and an operative position in which the releasable engagement arrangement is disengaged to allow extension of the second member. The release member can be manually moved to the operative position via a manual actuator arrangement, which may be in the form of a cable, chain or the like, that can be pulled by an operator so as to pivot the release member from the inoperative position to the operative position. In addition, the release member may be movable to the operative position in response to application of an upward force on the ramp while the ramp is in a lowered position, e.g. as a result of the truck bed moving upwardly during loading or unloading of the truck. In the past, the automatic release arrangement has included a length of chain connected at one end to a pin through which the first member of the holddown mechanism is mounted to the base, and connected at another end to an outer end defined by the release member. The chain is intended to operate as an automatic release actuator to move the release member to the operative position when an upward force is applied on the ramp, to enable the second member to be extended and to thereby allow the ramp to be raised under the influence of the biasing arrangement. While a fixed length chain of this type is capable of providing satisfactory operation of an automatic release mechanism, it has been found that, in practice, this type of automatic release actuator provides unpredictable and inconsistent performance, primarily due to the large number of high tolerance components (i.e. components that do not have closely controlled tolerances) incorporated in the release mechanism and the chain and the hardware used to mount the chain. Such lack of close tolerances can significantly affect the overall length of the actuator, which can result in the effective disablement of the automatic release function or providing premature automatic release.
It is an object of the present invention to provide an improved automatic release function in a holddown mechanism incorporated in a dock leveler assembly. It is a further object of the invention to provide an automatic release mechanism which is capable of being adjusted so as to accommodate manufacturing tolerances or other variations in components incorporated in the automatic release mechanism. Yet another object of the invention is to provide such an automatic release mechanism which functions in a manner similar to prior art automatic release mechanisms. Yet another object of the invention is to provide such an automatic release mechanism which can be calibrated during manufacture and thereafter retrofitted into an existing dock leveler assembly. A still further object of the invention is to provide a method of calibrating or adjusting an automatic release mechanism so as to provide consistent and reliable operation, either during original manufacture of the dock leveler or when retrofitting an existing dock leveler with a replacement holddown assembly.
The present invention features an automatic release mechanism for a dock leveler assembly as described above. The dock leveler assembly includes a release member movably interconnected with one of the first and second members of the holddown mechanism, for movement between an inoperative position for maintaining the releasable engagement arrangement in an engaged position to prevent movement between the first and second members, and an operative position for moving the releasable engagement arrangement to a disengaged position for allowing movement between the first and second members. The automatic release mechanism of the present invention includes an adjustable actuator member that defines a first end interconnected with one of the first and second members, and a second end interconnected with the release member. The effective length of the actuator member between the first and second ends is adjustable, which enables variation in the inoperative position of the release member. This adjustability in the inoperative position of the release member functions to control the degree of movement of the release member that is required for moving the release member to the operative position, in which the release member moves the releasable engagement arrangement to the disengaged position for allowing movement between the first and second members of the holddown mechanism, and thereby upward movement of the ramp when an upward force is applied to the ramp.
The release member is pivotable between the operative and inoperative positions, and the second end of the adjustable actuator member is interconnected with the release member at a location offset from the pivot axis about which the release member is pivotable. When the ramp member is in a lowered position, application of an upward force above a predetermined threshold functions to apply tension to the actuator member so as to cause the actuator member to pivot the release member from the inoperative position to the operative position, so as to disengage the releasable engagement arrangement and to allow movement between the first and second members of the holddown assembly, and thereby movement of the ramp member away from the lowered position partially toward the raised position. When the applied upward force falls below the predetermined threshold, the release member returns to the inoperative position to allow engagement of the releasable engagement arrangement so as to maintain the relative position of the first and second members of the holddown mechanism.
The adjustable actuator member includes a threaded adjustment mechanism interposed between the fixed end of the holddown mechanism and the release member. The threaded adjustment mechanism includes a threaded adjustment member engaged with the second end of the actuator member, a sleeve member secured to the release member through which the threaded adjustment member extends, and a threaded receiver engaged with the threaded adjustment member and with the sleeve member. In this manner, rotation of the threaded receiver relative to the threaded adjustment member functions to vary the effective length of the actuator member, to adjust the degree of movement of the release member that is required in order to place the release member in the operative position.
In accordance with another aspect of the invention, the inoperative position of a release member in an automatic release mechanism is adjusted so as to control the degree of movement of the release member that is required to disengage the releasable engagement arrangement of the holddown mechanism. Adjustment in the inoperative position of the release member is carried out by varying the effective length of the automatic actuator member, preferably in accordance with the foregoing summary.
The invention also contemplates a dock leveler assembly incorporating an automatic release mechanism, also in accordance with the foregoing summary.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.